SUMMARY OF PROPOSED WORK: It appears that specific substitutions in the constant region of L-chains may relate to definitive sequences in the variable region. The correlation of Mcg type C-region substitutions with sequences in the hypervariable regions immediately following the cysteine residues at positions 22 and 90 will be made. The sequence of the Mcg-gamma-chain will be correlated with the X-Ray determined structure of Mcg-IgG to see the interaction relationships between the VLVL and VLHV of the Mcg Bence-Jones and IgG proteins, respectively. Efforts to isolate disulfide bonded peptides derived from L-chains and H-chains of IgM proteins other than the usual four chain (L2 microns 2) IgMs will be continued to determine whether an L3 microns 2 IgMs obtains as has been reported. The relation of the binding of the two subunits of human superoxide dismutase to the two sulfhydryl groups in each chain will be extended. Some sequence work will be carried out on the cyanogen bromide fragments of human alpha-Fetoprotein in attempts to determine their relationship to human serum albumin. The complete primary structure of horse erythrocyte carbonic anhydrase D will be completed and the delineation of the amino acid substitutions responsible for various polymorphic forms determined. BIBLIOGRAPHIC REFERENCES: A New Human lambda-Chain Constant Region Gene. Fett, J. W. and Deutsch, H. F., Fed. Proc. 34:954 (1975). A New lambda-Chain Gene. Fett, J. W. and Deutsch, H. F., Immunochemistry 12: 643 (1975).